WO 2012/038330 and WO 2013/156476 describe how flue gases/off-gases can be treated with the electropositive metals lithium or magnesium in order to give substances of value and high-level thermal energy and thereby to reduce the soiling of the atmosphere.
WO 2012/038330 demonstrates the reaction of CO2 with lithium to give substances of value such as carbon monoxide or acetylene, which can be reacted further to given methanol or other substances of value. The thermal energy released can be utilized to drive the methanol/CO2 separation or even to drive a steam generator.
Reactions and considerations that are relevant in this context include the following:2Li+CO2→Li2O+CO−314.9 kJ/mol (comparison: C+O2→CO2−393.5 kJ/mol)4Li+CO2→2Li2O+C−803.94 kJ/molC+CO2→2CO+172.5 kJ/mol; which can be converted into methanol2C+2Li→Li2C2; which can be converted into acetylene (ratio CO2:Li)Li2CO3+4C→Li2C2+3COLi2O+CO2→Li2CO3;Li2CO3→Li2O+CO2 at the relevant temperatures of around 1500° C.Enthalpies of formation (298K): Li2O=−597.90 kJ/mol;Li2CO3=−1215.87 kJ/mol.2Li+2CO2→Li2CO3+CO−539 kJ
After a hydrolysis, a strongly alkaline Li2CO3 suspension is obtained.Li2C2+H2O→HC≡CH+2LiOHLi2O+CO2→Li2CO3 
WO 2013/156476 sets out how the treatments of flue gas/waste gas may also include a desulfurization in view of the high solubility of lithium-sulfur-based salts and the low solubility of lithium carbonate:6Li+SO2→Li2S+2Li2O8Li+SO3→Li2S+3Li2OLi2O+SO2→Li2SO3−438.7 kJ/mol
The suspension obtained after the combustion of CO2 and SO2 with a forced oxidation, said suspension containing Li2CO3 and Li2SO4, must then be separated. Fortunately, all lithium-sulfur salts are readily soluble in water (e.g., lithium sulfate at 350 g/l at room temperature (about 25° C.)). In contrast to Na2S2O5, ready solubility is also possessed by Li2S2O5 or Li2SO3. This means that all sulfur compounds remain in solution, while Li2CO3 (solubility 13 g/l) is formed as a precipitate and can be obtained as a fairly pure product for return (see WO 2010/000681). The ready solubility of lithium sulfate here is in contrast with that of CaSO4 (2 g/l), which is prepared in a prior-art desulfurization process.
All of these process sequences end with a slightly wet, fairly pure lithium carbonate. The reduction of lithium carbonate to give metallic lithium may be achieved, for example, by reaction of the carbonate to give the chloride and by the subsequent electrolysis of a eutectic mixture of potassium/lithium chloride.Li2CO3+2HCl→2LiCl+H2O+CO2  1.                (reaction enthalpy: −96 kJ/molLi2CO3+Cl2→2LiCl+½O2+CO2  2.        (reaction enthalpy: ˜5 kJ/mol)        
In processes for preparation of lithium chloride for the production of lithium, customarily, either lithium carbonate or lithium hydroxide is caused to react with hydrochloric acid/hydrogen chloride acid in an aqueous solution. Following evaporation and crystallization, the crystals are isolated and dried, to give a highly hygroscopic anhydrous lithium chloride, as described in Jürgen Deberitz, Lithium, Die Bibliothek der Wissenschaft Vol. 2, pp. 37, 2006 (ISBN-13: 978-3-937889-36-8). A substantial difficulty in such a process, as set out in U.S. Pat. No. 6,048,507, is the high energy requirement of theoretically 30×103 kJ/kg. No attention at all has to date been paid to the energy source that is used for the chemical conversion.
A further process, which is described in CA 2340528 A1 and US 20130001097 A1, involves reacting lithium carbonate with chlorine gas to give anhydrous lithium chloride. Preparation of anhydrous lithium chloride from pulverulent lithium carbonate in a fluidized-bed reactor is described in WO 2014/005878.
There continues to be a demand for an improved process for the production of metal chloride from metal carbonate, improved not least in terms of energy.